Life in a Treehouse: How Rafinesque’s Big-Eared Bats Choose their Roosts

Study based in South Carolina's Congaree National Park

by Sarah Farmer, SRS Science Delivery • January 21, 2016

In the South Carolina Coastal Plain, Rafinesque’s big-eared bats often roost in the hollows of bottomland hardwoods. Photo by U.S. Fish and Wildlife Service.

In the Coastal Plain of South Carolina, Rafinesque’s big-eared bats often roost in tree hollows throughout the year. “Bats spend a good portion of their lives in roosts,” says U.S. Forest Service scientist Susan Loeb. “Roosts protect bats from predators, and are where bats interact socially, mate, and raise young.”

Rafinesque’s big-eared bats are declining throughout their range. One of the primary threats is loss of roosts. Loeb, a research ecologist at the Forest Service Southern Research Station, is second author of a new paper on how Rafinesque’s big-eared bats select trees to roost in. Jessica Lucas, who at the time was affiliated with Clemson University and the U.S. Geological Survey, led the study published in the journal Acta Chiropterologica.

The study took place in the largest old growth bottomland hardwood forest in the U.S. – Congaree National Park, South Carolina. Loeb and her colleagues searched for roost trees in the summers of 2006 and 2007. The scientists focused on cypress-tupelo bottomlands, along streams and swampy areas, and in areas that were similar to known bat habitat. “We used spotlights and mirrors to search for big-eared bats in trees with hollows or cavities near the base of their trunks,” says Loeb. Bats were also captured in mist nets, and then tracked with light-weight radio transmitters.

Up to 100 female Rafinesque’s big-eared bats may roost together when they have young, although most maternal colonies have about 40 individuals. “We located 43 roosts,” says Loeb. “Almost a third of those were maternal colonies.” Bats in maternal colonies and those that lived alone selected similar roosts. However, in the Congaree National Park, bats in maternal colonies spent less time in the same roost trees – female bats with young often moved to a new roost tree each day, while adult males sometimes stayed in the same tree for almost 4 days. Bats in maternal colonies were also more likely to use trees with openings in the upper part of the trunk, probably as a way to avoid predators.

All Rafinesque’s big-eared bats preferred roosting in water tupelo trees that had large diameters and large hollows in their trunks. About two thirds of the roost trees were in semi-permanently flooded areas, and the best roost trees were surrounded by other potential roost trees.

Perhaps because the Congaree National Park is a relatively pristine forest, landscape factors such as the amount of forest land, distance to opening, and distance to water, did not seem to affect roost selection. The study indicates that retaining large diameter, hollow trees in wetland areas will benefit Rafinesque’s big-eared bats. “The old-growth bottomland hardwood forest found in Congaree National Park likely represents precolonial conditions,” says Loeb. “Our results can serve as a benchmark for restoration of more disturbed sites.”